Multiple objects or multiple meshes per object
There is no definitive answer for this, it is mostly a matter of opinion with some consideration of making some steps easier and how blender performs.

While you are modeling a complex model, there are advantages to working with multiple objects :-


You can make linked duplicates of an object so that they all use the same mesh data, this lets you model one window and duplicate it, then changing one window changes all windows to match.
Modifiers can be used to create a piece of a larger model, this might only be a temporary object that can be combined once the modifiers are applied.
You can quickly go into local view of just the selected objects (press / on the numpad) so that everything else is hidden.
You can find objects by name (if you name them as you go) and hide multiple objects to make working on one part of your model easier. While you can hide parts of a single mesh, you need to manually select each part of the mesh to hide or select what you want to see and invert the selection and hide it.


When a model is complete, having 135 separate objects to represent a single spaceship can make it awkward to select and move around as one, so there is an advantage to combining the multiple objects into one, once the modeling is complete. This is quickly done by selecting them and pressing &#9096; CtrlJ.

Performance wise using larger scenes, blender will perform better with one object that has one million vertices than with 1000 objects that have 1000 vertices each. This answer might give more insight.